Tank-venting apparatus as well as a method and arrangement for checking the tightness thereof

Abstract

The invention is directed to a method of checking the tightness of a tank-venting apparatus for a motor vehicle having a fuel tank and an internal combustion engine including a lambda controller and an air intake pipe. The tank-venting apparatus includes an adsorption filter, a supply line interconnecting the adsorption filter and the fuel tank, a connecting line interconnecting the adsorption filter and the intake pipe and a tank-venting valve mounted in the connecting line between the adsorption filter and the intake pipe. The method includes the steps of: measuring the pressure difference between pressure in the tank and ambient pressure; when the tank-venting valve is opened, determining whether the pressure difference increases above a threshold value and whether a lean correction by the lambda controller is required; and, drawing the conclusion that the tank-venting apparatus leaks when neither a lean correction is determined nor the pressure difference exceeds the threshold value. The method is based on the recognition that, when the tank-venting valve is open, either an underpressure must build up in the tank or a lean correction must be determined by the lambda controller based on the fuel vaporizing in the tank. The method is very reliable by simultaneously carrying out these two checks.

What is claimed is: 
     
       1. A method of checking the tightness of a tank-venting apparatus for a motor vehicle having a fuel tank and an internal combustion engine including a lambda controller and an air intake pipe, the tank-venting apparatus including an adsorption filter, a supply line interconnecting the adsorption filter and the fuel tank, a connecting line interconnecting the adsorption filter and the intake pipe and a tank-venting valve mounted in the connecting line between the adsorption filter and the intake pipe, the method comprising the steps of: measuring the pressure difference between the pressure in the tank and the ambient pressure;   when the tank-venting valve is opened, determining whether the pressure difference increases above a threshold value and whether a lean correction by the lambda controller is required; and,   drawing the conclusion that the tank-venting apparatus leaks when neither a lean correction is determined nor the pressure difference exceeds said threshold value.   
     
     
       2. The method of claim 1, further comprising the steps of: opening and closing the tank-venting valve for a pregiven time span a multiple number of times;   continuously checking whether said pressure difference exceeds said threshold value;   forming a correlation between the open time spans of the tank-venting valve and the occurrences of said pressure difference exceeding said threshold value to thereby determine a correlation factor; and,   then drawing the conclusion that the tank is tight when the correlation factor exceeds a pregiven value.   
     
     
       3. In a motor vehicle which includes a fuel tank and an internal combustion engine having a lambda controller supplying an actuating signal, an intake pipe and a tank-venting apparatus, the tank-venting apparatus including an adsorption filter, a supply line interconnecting the adsorption filter and the fuel tank, a connecting line interconnecting the adsorption filter and the intake pipe and a tank-venting valve mounted in the connecting line between the adsorption filter and the intake pipe, an arrangement for checking the tightness of the tank-venting apparatus, the arrangement comprising: a pressure-difference sensor mounted on the fuel tank for measuring the pressure difference between the pressure in the tank and the ambient pressure and for providing a pressure-difference signal;   an evaluation unit having a first terminal for receiving said actuating signal and a second terminal for receiving said pressure-difference signal;   said evaluation unit further having a threshold value setting device for setting an underpressure threshold value; and,   said evaluation unit being adapted to provide a defect signal indicating a leak of the fuel tank when neither said actuating signal from said first terminal indicates a lean correction nor said pressure-difference signal from second terminal exceeds said threshold value set by said setting device.   
     
     
       4. A tank-venting apparatus for an internal combustion engine having an intake pipe and being equipped with a fuel tank, the tank-venting apparatus comprising: an adsorption filter having a suction end at which a suction end pressure is present;   a connecting line connecting said suction end to said intake pipe;   a supply line connecting said adsorption filter to said fuel tank;   a tank-venting valve connected into said connecting line;   a pressure-difference sensor mounted on said fuel tank for measuring the pressure difference between pressure in said fuel tank and ambient pressure for providing a signal indicative of said pressure difference; and,   said supply line having an end portion introduced into said adsorption filter in a manner to cause said suction end pressure to be present at said end portion of said supply line.